1. Field of the Invention
The present invention relates to an anti-skid apparatus for installation in a vehicle braking system to prevent the road wheels of the vehicle from locking in braking operation, and more particularly to an anti-skid apparatus wherein an electrically operated switchover valve is disposed within each braking circuit connecting a master cylinder to wheel brake cylinders to intermittently connect the wheel brake cylinders to a fluid reservoir of the master cylinder in response to a control signal applied thereto from an electric control circuit when the road wheels tend to be locked.
2. Description of the Prior Art
In Japanese patent publication No. 56-10219, there has been proposed such an anti-skid apparatus as described above wherein the master cylinder is arranged to be power-assisted by a hydraulic brake booster and wherein an electrically operated cut-off valve is disposed within the braking circuit between the master cylinder and the switchover value to interrupt the fluid under pressure from the master cylinder when activated in response to the control signal from the electric control circuit, and a check valve is disposed within a fluid circuit connecting the brake booster to the braking circuit between the cut-off valve and the switchover valve to permit the fluid under pressure supplied from the brake booster to the wheel brake cylinders therethrough during activation of the cut-off valve. In the anti-skid apparatus, it is advantageous that during activation of the cut-off valve the hydraulic fluid in the pressure chamber of the master cylinder remains without causing any consumption thereof to eliminate useless depression stroke of the brake pedal. However, the intermittent supply of the pressurized fluid from the brake booster causes fluctuation in power assist to the master cylinder, resulting in unpleasant shock on the brake pedal.